Merge remote-tracking branch 'upstream/master' into libcall

1 files changed, 727 insertions, 0 deletions

diff --git a/runtime/lua/vim/lsp/util.lua b/runtime/lua/vim/lsp/util.lua
new file mode 100644
index 0000000000..3798b30a46
--- /dev/null
+++ b/runtime/lua/vim/lsp/util.lua
@@ -0,0 +1,727 @@
+local protocol = require 'vim.lsp.protocol'
+local vim = vim
+local validate = vim.validate
+local api = vim.api
+local list_extend = vim.list_extend
+
+local M = {}
+
+local split = vim.split
+local function split_lines(value)
+  return split(value, '\n', true)
+end
+
+local function ok_or_nil(status, ...)
+  if not status then return end
+  return ...
+end
+local function npcall(fn, ...)
+  return ok_or_nil(pcall(fn, ...))
+end
+
+--- Find the longest shared prefix between prefix and word.
+-- e.g. remove_prefix("123tes", "testing") == "ting"
+local function remove_prefix(prefix, word)
+  local max_prefix_length = math.min(#prefix, #word)
+  local prefix_length = 0
+  for i = 1, max_prefix_length do
+    local current_line_suffix = prefix:sub(-i)
+    local word_prefix = word:sub(1, i)
+    if current_line_suffix == word_prefix then
+      prefix_length = i
+    end
+  end
+  return word:sub(prefix_length + 1)
+end
+
+-- TODO(ashkan) @performance this could do less copying.
+function M.set_lines(lines, A, B, new_lines)
+  -- 0-indexing to 1-indexing
+  local i_0 = A[1] + 1
+  local i_n = B[1] + 1
+  if not (i_0 >= 1 and i_0 <= #lines and i_n >= 1 and i_n <= #lines) then
+    error("Invalid range: "..vim.inspect{A = A; B = B; #lines, new_lines})
+  end
+  local prefix = ""
+  local suffix = lines[i_n]:sub(B[2]+1)
+  if A[2] > 0 then
+    prefix = lines[i_0]:sub(1, A[2])
+  end
+  local n = i_n - i_0 + 1
+  if n ~= #new_lines then
+    for _ = 1, n - #new_lines do table.remove(lines, i_0) end
+    for _ = 1, #new_lines - n do table.insert(lines, i_0, '') end
+  end
+  for i = 1, #new_lines do
+    lines[i - 1 + i_0] = new_lines[i]
+  end
+  if #suffix > 0 then
+    local i = i_0 + #new_lines - 1
+    lines[i] = lines[i]..suffix
+  end
+  if #prefix > 0 then
+    lines[i_0] = prefix..lines[i_0]
+  end
+  return lines
+end
+
+local function sort_by_key(fn)
+  return function(a,b)
+    local ka, kb = fn(a), fn(b)
+    assert(#ka == #kb)
+    for i = 1, #ka do
+      if ka[i] ~= kb[i] then
+        return ka[i] < kb[i]
+      end
+    end
+    -- every value must have been equal here, which means it's not less than.
+    return false
+  end
+end
+local edit_sort_key = sort_by_key(function(e)
+  return {e.A[1], e.A[2], e.i}
+end)
+
+function M.apply_text_edits(text_edits, bufnr)
+  if not next(text_edits) then return end
+  local start_line, finish_line = math.huge, -1
+  local cleaned = {}
+  for i, e in ipairs(text_edits) do
+    start_line = math.min(e.range.start.line, start_line)
+    finish_line = math.max(e.range["end"].line, finish_line)
+    -- TODO(ashkan) sanity check ranges for overlap.
+    table.insert(cleaned, {
+      i = i;
+      A = {e.range.start.line; e.range.start.character};
+      B = {e.range["end"].line; e.range["end"].character};
+      lines = vim.split(e.newText, '\n', true);
+    })
+  end
+
+  -- Reverse sort the orders so we can apply them without interfering with
+  -- eachother. Also add i as a sort key to mimic a stable sort.
+  table.sort(cleaned, edit_sort_key)
+  local lines = api.nvim_buf_get_lines(bufnr, start_line, finish_line + 1, false)
+  local fix_eol = api.nvim_buf_get_option(bufnr, 'fixeol')
+  local set_eol = fix_eol and api.nvim_buf_line_count(bufnr) == finish_line + 1
+  if set_eol and #lines[#lines] ~= 0 then
+    table.insert(lines, '')
+  end
+
+  for i = #cleaned, 1, -1 do
+    local e = cleaned[i]
+    local A = {e.A[1] - start_line, e.A[2]}
+    local B = {e.B[1] - start_line, e.B[2]}
+    lines = M.set_lines(lines, A, B, e.lines)
+  end
+  if set_eol and #lines[#lines] == 0 then
+    table.remove(lines)
+  end
+  api.nvim_buf_set_lines(bufnr, start_line, finish_line + 1, false, lines)
+end
+
+-- local valid_windows_path_characters = "[^<>:\"/\\|?*]"
+-- local valid_unix_path_characters = "[^/]"
+-- https://github.com/davidm/lua-glob-pattern
+-- https://stackoverflow.com/questions/1976007/what-characters-are-forbidden-in-windows-and-linux-directory-names
+-- function M.glob_to_regex(glob)
+-- end
+
+-- textDocument/completion response returns one of CompletionItem[], CompletionList or null.
+-- https://microsoft.github.io/language-server-protocol/specification#textDocument_completion
+function M.extract_completion_items(result)
+  if type(result) == 'table' and result.items then
+    return result.items
+  elseif result ~= nil then
+    return result
+  else
+    return {}
+  end
+end
+
+--- Apply the TextDocumentEdit response.
+-- @params TextDocumentEdit [table] see https://microsoft.github.io/language-server-protocol/specification
+function M.apply_text_document_edit(text_document_edit)
+  local text_document = text_document_edit.textDocument
+  local bufnr = vim.uri_to_bufnr(text_document.uri)
+  -- TODO(ashkan) check this is correct.
+  if api.nvim_buf_get_changedtick(bufnr) > text_document.version then
+    print("Buffer ", text_document.uri, " newer than edits.")
+    return
+  end
+  M.apply_text_edits(text_document_edit.edits, bufnr)
+end
+
+function M.get_current_line_to_cursor()
+  local pos = api.nvim_win_get_cursor(0)
+  local line = assert(api.nvim_buf_get_lines(0, pos[1]-1, pos[1], false)[1])
+  return line:sub(pos[2]+1)
+end
+
+--- Getting vim complete-items with incomplete flag.
+-- @params CompletionItem[], CompletionList or nil (https://microsoft.github.io/language-server-protocol/specification#textDocument_completion)
+-- @return { matches = complete-items table, incomplete = boolean  }
+function M.text_document_completion_list_to_complete_items(result, line_prefix)
+  local items = M.extract_completion_items(result)
+  if vim.tbl_isempty(items) then
+    return {}
+  end
+  -- Only initialize if we have some items.
+  if not line_prefix then
+    line_prefix = M.get_current_line_to_cursor()
+  end
+
+  local matches = {}
+
+  for _, completion_item in ipairs(items) do
+    local info = ' '
+    local documentation = completion_item.documentation
+    if documentation then
+      if type(documentation) == 'string' and documentation ~= '' then
+        info = documentation
+      elseif type(documentation) == 'table' and type(documentation.value) == 'string' then
+        info = documentation.value
+      -- else
+        -- TODO(ashkan) Validation handling here?
+      end
+    end
+
+    local word = completion_item.insertText or completion_item.label
+
+    -- Ref: `:h complete-items`
+    table.insert(matches, {
+      word = remove_prefix(line_prefix, word),
+      abbr = completion_item.label,
+      kind = protocol.CompletionItemKind[completion_item.kind] or '',
+      menu = completion_item.detail or '',
+      info = info,
+      icase = 1,
+      dup = 0,
+      empty = 1,
+    })
+  end
+
+  return matches
+end
+
+-- @params WorkspaceEdit [table] see https://microsoft.github.io/language-server-protocol/specification
+function M.apply_workspace_edit(workspace_edit)
+  if workspace_edit.documentChanges then
+    for _, change in ipairs(workspace_edit.documentChanges) do
+      if change.kind then
+        -- TODO(ashkan) handle CreateFile/RenameFile/DeleteFile
+        error(string.format("Unsupported change: %q", vim.inspect(change)))
+      else
+        M.apply_text_document_edit(change)
+      end
+    end
+    return
+  end
+
+  local all_changes = workspace_edit.changes
+  if not (all_changes and not vim.tbl_isempty(all_changes)) then
+    return
+  end
+
+  for uri, changes in pairs(all_changes) do
+    local bufnr = vim.uri_to_bufnr(uri)
+    M.apply_text_edits(changes, bufnr)
+  end
+end
+
+--- Convert any of MarkedString | MarkedString[] | MarkupContent into markdown text lines
+-- see https://microsoft.github.io/language-server-protocol/specifications/specification-3-14/#textDocument_hover
+-- Useful for textDocument/hover, textDocument/signatureHelp, and potentially others.
+function M.convert_input_to_markdown_lines(input, contents)
+  contents = contents or {}
+  -- MarkedString variation 1
+  if type(input) == 'string' then
+    list_extend(contents, split_lines(input))
+  else
+    assert(type(input) == 'table', "Expected a table for Hover.contents")
+    -- MarkupContent
+    if input.kind then
+      -- The kind can be either plaintext or markdown. However, either way we
+      -- will just be rendering markdown, so we handle them both the same way.
+      -- TODO these can have escaped/sanitized html codes in markdown. We
+      -- should make sure we handle this correctly.
+
+      -- Some servers send input.value as empty, so let's ignore this :(
+      -- assert(type(input.value) == 'string')
+      list_extend(contents, split_lines(input.value or ''))
+    -- MarkupString variation 2
+    elseif input.language then
+      -- Some servers send input.value as empty, so let's ignore this :(
+      -- assert(type(input.value) == 'string')
+      table.insert(contents, "```"..input.language)
+      list_extend(contents, split_lines(input.value or ''))
+      table.insert(contents, "```")
+    -- By deduction, this must be MarkedString[]
+    else
+      -- Use our existing logic to handle MarkedString
+      for _, marked_string in ipairs(input) do
+        M.convert_input_to_markdown_lines(marked_string, contents)
+      end
+    end
+  end
+  if contents[1] == '' or contents[1] == nil then
+    return {}
+  end
+  return contents
+end
+
+function M.make_floating_popup_options(width, height, opts)
+  validate {
+    opts = { opts, 't', true };
+  }
+  opts = opts or {}
+  validate {
+    ["opts.offset_x"] = { opts.offset_x, 'n', true };
+    ["opts.offset_y"] = { opts.offset_y, 'n', true };
+  }
+
+  local anchor = ''
+  local row, col
+
+  if vim.fn.winline() <= height then
+    anchor = anchor..'N'
+    row = 1
+  else
+    anchor = anchor..'S'
+    row = 0
+  end
+
+  if vim.fn.wincol() + width <= api.nvim_get_option('columns') then
+    anchor = anchor..'W'
+    col = 0
+  else
+    anchor = anchor..'E'
+    col = 1
+  end
+
+  return {
+    anchor = anchor,
+    col = col + (opts.offset_x or 0),
+    height = height,
+    relative = 'cursor',
+    row = row + (opts.offset_y or 0),
+    style = 'minimal',
+    width = width,
+  }
+end
+
+function M.jump_to_location(location)
+  if location.uri == nil then return end
+  local bufnr = vim.uri_to_bufnr(location.uri)
+  -- Save position in jumplist
+  vim.cmd "normal! m'"
+  -- TODO(ashkan) use tagfunc here to update tagstack.
+  api.nvim_set_current_buf(bufnr)
+  local row = location.range.start.line
+  local col = location.range.start.character
+  local line = api.nvim_buf_get_lines(0, row, row+1, true)[1]
+  col = vim.str_byteindex(line, col)
+  api.nvim_win_set_cursor(0, {row + 1, col})
+  return true
+end
+
+local function find_window_by_var(name, value)
+  for _, win in ipairs(api.nvim_list_wins()) do
+    if npcall(api.nvim_win_get_var, win, name) == value then
+      return win
+    end
+  end
+end
+
+-- Check if a window with `unique_name` tagged is associated with the current
+-- buffer. If not, make a new preview.
+--
+-- fn()'s return values will be passed directly to open_floating_preview in the
+-- case that a new floating window should be created.
+function M.focusable_preview(unique_name, fn)
+  if npcall(api.nvim_win_get_var, 0, unique_name) then
+    return api.nvim_command("wincmd p")
+  end
+  local bufnr = api.nvim_get_current_buf()
+  do
+    local win = find_window_by_var(unique_name, bufnr)
+    if win then
+      api.nvim_set_current_win(win)
+      api.nvim_command("stopinsert")
+      return
+    end
+  end
+  local pbufnr, pwinnr = M.open_floating_preview(fn())
+  api.nvim_win_set_var(pwinnr, unique_name, bufnr)
+  return pbufnr, pwinnr
+end
+
+function M.open_floating_preview(contents, filetype, opts)
+  validate {
+    contents = { contents, 't' };
+    filetype = { filetype, 's', true };
+    opts = { opts, 't', true };
+  }
+  opts = opts or {}
+
+  -- Trim empty lines from the end.
+  contents = M.trim_empty_lines(contents)
+
+  local width = opts.width
+  local height = opts.height or #contents
+  if not width then
+    width = 0
+    for i, line in ipairs(contents) do
+      -- Clean up the input and add left pad.
+      line = " "..line:gsub("\r", "")
+      -- TODO(ashkan) use nvim_strdisplaywidth if/when that is introduced.
+      local line_width = vim.fn.strdisplaywidth(line)
+      width = math.max(line_width, width)
+      contents[i] = line
+    end
+    -- Add right padding of 1 each.
+    width = width + 1
+  end
+
+  local floating_bufnr = api.nvim_create_buf(false, true)
+  if filetype then
+    api.nvim_buf_set_option(floating_bufnr, 'filetype', filetype)
+  end
+  local float_option = M.make_floating_popup_options(width, height, opts)
+  local floating_winnr = api.nvim_open_win(floating_bufnr, false, float_option)
+  if filetype == 'markdown' then
+    api.nvim_win_set_option(floating_winnr, 'conceallevel', 2)
+  end
+  api.nvim_buf_set_lines(floating_bufnr, 0, -1, true, contents)
+  api.nvim_buf_set_option(floating_bufnr, 'modifiable', false)
+  -- TODO make InsertCharPre disappearing optional?
+  api.nvim_command("autocmd CursorMoved,BufHidden,InsertCharPre <buffer> ++once lua pcall(vim.api.nvim_win_close, "..floating_winnr..", true)")
+  return floating_bufnr, floating_winnr
+end
+
+local function validate_lsp_position(pos)
+  validate { pos = {pos, 't'} }
+  validate {
+    line = {pos.line, 'n'};
+    character = {pos.character, 'n'};
+  }
+  return true
+end
+
+function M.open_floating_peek_preview(bufnr, start, finish, opts)
+  validate {
+    bufnr = {bufnr, 'n'};
+    start = {start, validate_lsp_position, 'valid start Position'};
+    finish = {finish, validate_lsp_position, 'valid finish Position'};
+    opts = { opts, 't', true };
+  }
+  local width = math.max(finish.character - start.character + 1, 1)
+  local height = math.max(finish.line - start.line + 1, 1)
+  local floating_winnr = api.nvim_open_win(bufnr, false, M.make_floating_popup_options(width, height, opts))
+  api.nvim_win_set_cursor(floating_winnr, {start.line+1, start.character})
+  api.nvim_command("autocmd CursorMoved * ++once lua pcall(vim.api.nvim_win_close, "..floating_winnr..", true)")
+  return floating_winnr
+end
+
+
+local function highlight_range(bufnr, ns, hiname, start, finish)
+  if start[1] == finish[1] then
+    -- TODO care about encoding here since this is in byte index?
+    api.nvim_buf_add_highlight(bufnr, ns, hiname, start[1], start[2], finish[2])
+  else
+    api.nvim_buf_add_highlight(bufnr, ns, hiname, start[1], start[2], -1)
+    for line = start[1] + 1, finish[1] - 1 do
+      api.nvim_buf_add_highlight(bufnr, ns, hiname, line, 0, -1)
+    end
+    api.nvim_buf_add_highlight(bufnr, ns, hiname, finish[1], 0, finish[2])
+  end
+end
+
+do
+  local all_buffer_diagnostics = {}
+
+  local diagnostic_ns = api.nvim_create_namespace("vim_lsp_diagnostics")
+
+  local underline_highlight_name = "LspDiagnosticsUnderline"
+  api.nvim_command(string.format("highlight default %s gui=underline cterm=underline", underline_highlight_name))
+
+  local severity_highlights = {}
+
+  local default_severity_highlight = {
+    [protocol.DiagnosticSeverity.Error] = { guifg = "Red" };
+    [protocol.DiagnosticSeverity.Warning] = { guifg = "Orange" };
+    [protocol.DiagnosticSeverity.Information] = { guifg = "LightBlue" };
+    [protocol.DiagnosticSeverity.Hint] = { guifg = "LightGrey" };
+  }
+
+  -- Initialize default severity highlights
+  for severity, hi_info in pairs(default_severity_highlight) do
+    local severity_name = protocol.DiagnosticSeverity[severity]
+    local highlight_name = "LspDiagnostics"..severity_name
+    -- Try to fill in the foreground color with a sane default.
+    local cmd_parts = {"highlight", "default", highlight_name}
+    for k, v in pairs(hi_info) do
+      table.insert(cmd_parts, k.."="..v)
+    end
+    api.nvim_command(table.concat(cmd_parts, ' '))
+    severity_highlights[severity] = highlight_name
+  end
+
+  function M.buf_clear_diagnostics(bufnr)
+    validate { bufnr = {bufnr, 'n', true} }
+    bufnr = bufnr == 0 and api.nvim_get_current_buf() or bufnr
+    api.nvim_buf_clear_namespace(bufnr, diagnostic_ns, 0, -1)
+  end
+
+  function M.get_severity_highlight_name(severity)
+    return severity_highlights[severity]
+  end
+
+  function M.show_line_diagnostics()
+    local bufnr = api.nvim_get_current_buf()
+    local line = api.nvim_win_get_cursor(0)[1] - 1
+    -- local marks = api.nvim_buf_get_extmarks(bufnr, diagnostic_ns, {line, 0}, {line, -1}, {})
+    -- if #marks == 0 then
+    --   return
+    -- end
+    -- local buffer_diagnostics = all_buffer_diagnostics[bufnr]
+    local lines = {"Diagnostics:"}
+    local highlights = {{0, "Bold"}}
+
+    local buffer_diagnostics = all_buffer_diagnostics[bufnr]
+    if not buffer_diagnostics then return end
+    local line_diagnostics = buffer_diagnostics[line]
+    if not line_diagnostics then return end
+
+    for i, diagnostic in ipairs(line_diagnostics) do
+    -- for i, mark in ipairs(marks) do
+    --   local mark_id = mark[1]
+    --   local diagnostic = buffer_diagnostics[mark_id]
+
+      -- TODO(ashkan) make format configurable?
+      local prefix = string.format("%d. ", i)
+      local hiname = severity_highlights[diagnostic.severity]
+      local message_lines = split_lines(diagnostic.message)
+      table.insert(lines, prefix..message_lines[1])
+      table.insert(highlights, {#prefix + 1, hiname})
+      for j = 2, #message_lines do
+        table.insert(lines, message_lines[j])
+        table.insert(highlights, {0, hiname})
+      end
+    end
+    local popup_bufnr, winnr = M.open_floating_preview(lines, 'plaintext')
+    for i, hi in ipairs(highlights) do
+      local prefixlen, hiname = unpack(hi)
+      -- Start highlight after the prefix
+      api.nvim_buf_add_highlight(popup_bufnr, -1, hiname, i-1, prefixlen, -1)
+    end
+    return popup_bufnr, winnr
+  end
+
+  function M.buf_diagnostics_save_positions(bufnr, diagnostics)
+    validate {
+      bufnr = {bufnr, 'n', true};
+      diagnostics = {diagnostics, 't', true};
+    }
+    if not diagnostics then return end
+    bufnr = bufnr == 0 and api.nvim_get_current_buf() or bufnr
+
+    if not all_buffer_diagnostics[bufnr] then
+      -- Clean up our data when the buffer unloads.
+      api.nvim_buf_attach(bufnr, false, {
+        on_detach = function(b)
+          all_buffer_diagnostics[b] = nil
+        end
+      })
+    end
+    all_buffer_diagnostics[bufnr] = {}
+    local buffer_diagnostics = all_buffer_diagnostics[bufnr]
+
+    for _, diagnostic in ipairs(diagnostics) do
+      local start = diagnostic.range.start
+      -- local mark_id = api.nvim_buf_set_extmark(bufnr, diagnostic_ns, 0, start.line, 0, {})
+      -- buffer_diagnostics[mark_id] = diagnostic
+      local line_diagnostics = buffer_diagnostics[start.line]
+      if not line_diagnostics then
+        line_diagnostics = {}
+        buffer_diagnostics[start.line] = line_diagnostics
+      end
+      table.insert(line_diagnostics, diagnostic)
+    end
+  end
+
+
+  function M.buf_diagnostics_underline(bufnr, diagnostics)
+    for _, diagnostic in ipairs(diagnostics) do
+      local start = diagnostic.range.start
+      local finish = diagnostic.range["end"]
+
+      -- TODO care about encoding here since this is in byte index?
+      highlight_range(bufnr, diagnostic_ns, underline_highlight_name,
+          {start.line, start.character},
+          {finish.line, finish.character}
+      )
+    end
+  end
+
+  function M.buf_diagnostics_virtual_text(bufnr, diagnostics)
+    local buffer_line_diagnostics = all_buffer_diagnostics[bufnr]
+    if not buffer_line_diagnostics then
+      M.buf_diagnostics_save_positions(bufnr, diagnostics)
+    end
+    buffer_line_diagnostics = all_buffer_diagnostics[bufnr]
+    if not buffer_line_diagnostics then
+      return
+    end
+    for line, line_diags in pairs(buffer_line_diagnostics) do
+      local virt_texts = {}
+      for i = 1, #line_diags - 1 do
+        table.insert(virt_texts, {"■", severity_highlights[line_diags[i].severity]})
+      end
+      local last = line_diags[#line_diags]
+      -- TODO(ashkan) use first line instead of subbing 2 spaces?
+      table.insert(virt_texts, {"■ "..last.message:gsub("\r", ""):gsub("\n", "  "), severity_highlights[last.severity]})
+      api.nvim_buf_set_virtual_text(bufnr, diagnostic_ns, line, virt_texts, {})
+    end
+  end
+end
+
+local position_sort = sort_by_key(function(v)
+  return {v.line, v.character}
+end)
+
+-- Returns the items with the byte position calculated correctly and in sorted
+-- order.
+function M.locations_to_items(locations)
+  local items = {}
+  local grouped = setmetatable({}, {
+    __index = function(t, k)
+      local v = {}
+      rawset(t, k, v)
+      return v
+    end;
+  })
+  for _, d in ipairs(locations) do
+    local start = d.range.start
+    local fname = assert(vim.uri_to_fname(d.uri))
+    table.insert(grouped[fname], start)
+  end
+  local keys = vim.tbl_keys(grouped)
+  table.sort(keys)
+  -- TODO(ashkan) I wish we could do this lazily.
+  for _, fname in ipairs(keys) do
+    local rows = grouped[fname]
+    table.sort(rows, position_sort)
+    local i = 0
+    for line in io.lines(fname) do
+      for _, pos in ipairs(rows) do
+        local row = pos.line
+        if i == row then
+          local col
+          if pos.character > #line then
+            col = #line
+          else
+            col = vim.str_byteindex(line, pos.character)
+          end
+          table.insert(items, {
+            filename = fname,
+            lnum = row + 1,
+            col = col + 1;
+            text = line;
+          })
+        end
+      end
+      i = i + 1
+    end
+  end
+  return items
+end
+
+-- locations is Location[]
+-- Only sets for the current window.
+function M.set_loclist(locations)
+  vim.fn.setloclist(0, {}, ' ', {
+    title = 'Language Server';
+    items = M.locations_to_items(locations);
+  })
+end
+
+-- locations is Location[]
+function M.set_qflist(locations)
+  vim.fn.setqflist({}, ' ', {
+    title = 'Language Server';
+    items = M.locations_to_items(locations);
+  })
+end
+
+-- Remove empty lines from the beginning and end.
+function M.trim_empty_lines(lines)
+  local start = 1
+  for i = 1, #lines do
+    if #lines[i] > 0 then
+      start = i
+      break
+    end
+  end
+  local finish = 1
+  for i = #lines, 1, -1 do
+    if #lines[i] > 0 then
+      finish = i
+      break
+    end
+  end
+  return vim.list_extend({}, lines, start, finish)
+end
+
+-- Accepts markdown lines and tries to reduce it to a filetype if it is
+-- just a single code block.
+-- Note: This modifies the input.
+--
+-- Returns: filetype or 'markdown' if it was unchanged.
+function M.try_trim_markdown_code_blocks(lines)
+  local language_id = lines[1]:match("^```(.*)")
+  if language_id then
+    local has_inner_code_fence = false
+    for i = 2, (#lines - 1) do
+      local line = lines[i]
+      if line:sub(1,3) == '```' then
+        has_inner_code_fence = true
+        break
+      end
+    end
+    -- No inner code fences + starting with code fence = hooray.
+    if not has_inner_code_fence then
+      table.remove(lines, 1)
+      table.remove(lines)
+      return language_id
+    end
+  end
+  return 'markdown'
+end
+
+local str_utfindex = vim.str_utfindex
+function M.make_position_params()
+  local row, col = unpack(api.nvim_win_get_cursor(0))
+  row = row - 1
+  local line = api.nvim_buf_get_lines(0, row, row+1, true)[1]
+  col = str_utfindex(line, col)
+  return {
+    textDocument = { uri = vim.uri_from_bufnr(0) };
+    position = { line = row; character = col; }
+  }
+end
+
+-- @param buf buffer handle or 0 for current.
+-- @param row 0-indexed line
+-- @param col 0-indexed byte offset in line
+function M.character_offset(buf, row, col)
+  local line = api.nvim_buf_get_lines(buf, row, row+1, true)[1]
+  -- If the col is past the EOL, use the line length.
+  if col > #line then
+    return str_utfindex(line)
+  end
+  return str_utfindex(line, col)
+end
+
+return M
+-- vim:sw=2 ts=2 et